The present disclosure relates to a positively chargeable electrophotographic photosensitive member and an image forming apparatus using the same.
An electrophotographic image forming apparatus includes an electrophotographic photosensitive member. Examples of electrophotographic photosensitive members include inorganic photosensitive members and organic photosensitive members. An inorganic photosensitive member includes a photosensitive layer containing an inorganic material such as selenium or amorphous silicon. An organic photosensitive member includes a photosensitive layer mainly containing an organic material such as a binder resin, a charge generating material, and a charge transport material. Organic photosensitive members are widely used for the following reason. That is, organic photosensitive members can be produced more easily than inorganic photosensitive members and allow materials for the photosensitive layer to be selected from a wide variety of materials, providing high design flexibility.
Examples of such photosensitive members include negatively chargeable photosensitive members and positively chargeable photosensitive members. As compared with the positively chargeable photosensitive members, the negatively chargeable photosensitive members are problematic in that corona discharge utilized at the time of charging may be instable and that ozone, nitrogen oxide, and the like may be generated and adhere to the surface of the photosensitive members, which tends to result in physical and chemical degradation, or environmental degradation. From these standpoints, positively chargeable photosensitive members are more advantageous than negatively chargeable photosensitive members because of its greater flexibility in the conditions of use and its wider application range.
As such a positively chargeable photosensitive member, suggestion is made to use a positively chargeable multi-layered electrophotographic photosensitive member in which, for example, a charge generating layer is disposed on a charge transport layer. This layer structure is in reverse of a typical negatively chargeable multi-layered electrophotographic photosensitive member. However, the charge transport layer needs to contain as a charge transport material a hole transport material, which has excellent charge transport capability. In this case, the charge generating layer is disposed to form a top surface of the positively chargeable multi-layered electrophotographic photosensitive member. As a result, the charge generating layer may abrade to cause a significant change in its characteristics, which may lead to a problem that a sufficient durability is failed to be ensured.
A positively chargeable single-layer electrophotographic photosensitive member includes a photosensitive layer containing both an electron transport material and a hole transport material as the charge transport material. Thus, the photosensitive member has sensitivity to both the positive and negative charges. For this reason, single-layer electrophotographic photosensitive members are currently in the mainstream of electrophotographic photosensitive members of a positively chargeable type.